1. Field of the Invention
The invention relates to an inkjet printhead, and particularly to an inkjet printhead formed by positioning and laminating an actuator to a cavity unit in which a plurality of nozzles are formed, and a method of assembling such an inkjet printhead.
2. Description of Related Art
As a conventional inkjet printhead, there is known a piezoelectric inkjet printhead, as disclosed in FIGS. 3, 8 and 9 of JP-A-2003-112423 applied by the present applicant, for instance, which comprises a cavity unit having a plurality of nozzles and a plurality of pressure chambers respectively corresponding to the nozzles, a planar piezoelectric actuator having a plurality of active portions respectively corresponding to the pressure chambers, and a flexible flat cable for supplying power to the piezoelectric actuator.
The cavity unit is formed by stacking and bonding to one another a nozzle plate with the nozzles formed therethrough, a cavity plate where a plurality of through-holes providing the pressure chambers are formed, and other plates each with a plurality of ink passages, such as those providing a plurality of common ink chambers, formed therethrough. The piezoelectric actuator is formed by alternately stacking and bonding a plurality of piezoelectric sheets on each of which a plurality of individual electrodes are formed, and a plurality of piezoelectric sheets on each of which a common electrode common to a group of pressure chambers is formed. Each portion sandwiched between an individual electrode and a common electrode serves as an active portion.
The piezoelectric actuator is superposed on and bonded to the cavity unit such that the pressure chambers positionally correspond to the respective active portions. Further, a flexible flat cable is superposed on and bonded to the piezoelectric actuator so as to be capable of selectively supplying power to the individual electrodes. When a particular active portion is supplied with power and contacts, the contraction deforms a corresponding one of the pressure chambers so as to eject a droplet of ink from a nozzle in communication with the pressure chamber.
In the inkjet printhead constructed as described above, the ejection of ink droplets from the nozzles is greatly affected by the degree of alignment of the active portions with the pressure chambers, the piezoelectric actuator and the cavity unit should be positioned relatively each other with a high accuracy and precision.
Thus, the present applicant has proposed in the above-mentioned publication, a way of positioning a piezoelectric actuator and a cavity unit relatively to each other accurately and precisely. That is, a reference point of the piezoelectric actuator 12 as has been fired is accurately and precisely obtained with an image processor, based on four detection portions that are respectively formed at four corners of the piezoelectric actuator, and similarly, a reference point of the cavity unit is similarly obtained, based on four detection portions that are respectively formed at four corners of the cavity unit. Then, the piezoelectric actuator and the cavity unit are moved relatively to each other so that these reference points are aligned. In this way, an accurate and precise positioning between the piezoelectric actuator and the cavity unit is realized.
The plates constituting the cavity unit are typically formed of metal, since the ink passages and others are usually formed by etching. Thus, the cavity unit does not allow light to pass therethrough in a direction of stacking of the plates. Hence, the present applicant has proposed to provide detection portions in the form of four small holes, in a topmost one of the plates of the cavity unit, and acquire the position of the holes by processing, by an image processor, an image obtained by irradiating the cavity unit at each of the positions where the holes are formed, from the upper side of the cavity unit that corresponds to an back or inner side of the cavity unit that is remote from a nozzle surface thereof in which the nozzles are arranged.
However, the above-described technique suffers from a problem that the holes serving as detection portions are recognized based on light reflected from the cavity unit, and accordingly the obtained images are low in contrast. In addition, since the plates of the cavity unit have flaws such as streaks made during rolling, where the detection of the holes is performed by directly irradiating with light an inner or back surface of the cavity unit in which the hole is formed, the image processor tends to erroneously recognize the contour of each hole due to the presence of the flaws, leading to low accuracy and low preciseness in detecting the detection portions of the cavity unit.